U.S. Pat. No. 4,036,486, incorporated herein by reference, describes a mat board cutter by which a mat board is cut to have a desired peripheral size to fit within a desired frame and to have a desired central opening through which a picture being framed is visible.
As described in greater detail in U.S. Pat. No. 4,036,486, cutting the mat board requires sliding a cutter-carrying body along a path defined by a guide rail with a knife on a cutter device pivotably carried on the body in engagement with the mat, which mat is held in a predetermined position by abutment means on a base and a clamp bar having an upper surface along which the guide rail is mounted. The body has a channel that is defined by an almost fully cylindrical surface, opens through end surfaces and a bottom surface of the body, and receives the rail. The almost fully cylindrical surface provides (or supports a structure such as a strip of tape that provides) a bearing surface which engages a guide surface along the rail to insure that the body accurately slides along the path defined by the rail, since movement other than linear sliding movement of the body along the rail can result in an irregular or non-linear cut edge on the mat board. A body 10 for one less expensive variety of such a mat board cutter sold under the trade designation "Art Mate" by Minnesota Mining and Manufacturing Company, Saint Paul, Minnesota, is shown in FIG. 1 of the drawing. That body 10 has an almost fully cylindrical surface 12 defining such a channel, which surface 12 has a sufficiently large diameter to provide clearance between the surface 12 and a guide surface on a cylindrical rail (not shown) along which the body is guided. Several lengths 16 of pressure sensitive adhesive coated "teflon" tape are applied to the body 10 along the surface 12 and a bottom surface 18 of the body 10 to provide bearing surfaces for the body 10 against the guide surface of the rail and the upper surface of the clamp bar under the rail to afford accurate linear movement of the body along the rail. With use, however, wear on the lengths 16 of tape, or pealing away of one or more of the lengths 16 of tape can allow the body 10 to be moved out of its intended path defined by the rail so that cuts made by the knife are not as straight as may be desired.